Instrument moving-coil assemblies



Dec. 23, 1958 D. A. YOUNG INSTRUMENT MOVING-COIL ASSEMBLIES Filed June 26, 1953 WITNESSES:

@M 1,. Mm

I28A Fig.2 U

33 28 29 so 26 32 34 24 I8 3 I36 us A30 INVENTOR Douglass A.Young.

ATTORNEY Sttes INSTRUMENT MOVING-COIL ASSEMBLIES Application June 26, 1953, Serial No. 364,451

3 Claims. (Cl. 317-166) This invention relates to moving-coil assemblies for electrical instruments and more particularly to movingcoil assemblies including coils mounted for rotation relative to magnetic structures defining air gaps for the moving coils.

In accordance with the invention, a moving-coil assembly is provided which includes a composite shaft adapted to support a substantially rectangular coil structure concentrically thereof for rotation relative to the magnetic structure of an electrical instrument. The composite shaft includes a central coil-supporting member having stub shafts secured thereto with the stub shafts and the support member being disposed along a common axis. Each stub shaft may be provided with an aperture at the free end thereof proportioned to receive suitable pivots which support the composite shaft for rotation. To facilitate mounting of the coil structure, the supporting member may be provided with an opening proportioned to receive a side portion of the coil structure. The coil structure is positioned concentrically of the supporting member with portions of the end portions thereof within the opening of the support member adjacent the end walls thereof. The coil structure is secured to the support member by any suitable means, but preferably each end portion of the coil structure has portions thereof embedded within an insulating plastic mass which engages the terminals of the support member adjacent the end walls of the opening thereof.

It is, therefore, an object of the invention to provide an improved moving-coil assembly for electrical instruments.

It is another object of the invention to provide a moving-coil assembly including a composite shaft having a central coil-supporting member with a pair of stub shafts secured thereto.

It is still another object of the invention to provide a moving-coil assembly including a composite shaft adapted to support a coil structure concentrically thereof with no portion of the shaft being positioned between windings of the coil structure.

Other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawings in which:

Fig. l is a view in perspective with parts broken away of an electrical measuring instrument embodying the invention;

Fig. 2 is a view in front elevation of the moving-coil assembly of the instrument of Fig. 1 with portions thereof shown in section.

Fig. 3 is a view in section taken along the line III III of Fig. 2;

Fig. 4 is a view in front elevation of the coil-supporting member of the assembly of Figs. 2 and 3;

Fig. 5 is a view in side elevation of the member of Fig. 4;

Fig. 6 is a view in top plan of the member of Fig. 5.

Referring to the drawing, Fig. 1 shows. an electrodynamometer instrument of the type shown and described atent in Patent No. 2,508,410 issued on May 23, 1950, to L. J. Lunas. It is to be understood that applicants movingcoil assembly may be utilized with other types of instruments, such as direct current, permanent magnet instruments. As shown in Fig. 1, the instrument may include a stator assembly 2 and a rotor assembly 4.

The rotor assembly 4 comprises a moving-coil assembly which will be described in detail hereinafter. As shown in Fig. 1, the moving-coil assembly includes a composite shaft 6 mounted for rotation by hearing screws 8 and 10 which constitute portions of the stator assembly 2. The shaft 6 is adapted to support a coil structure 12 disposed in a loop with side portions 14 and 16 and end portions 18 and 20 connecting the side portions. As shown, the coil sides 14 and 16 are disposed parallel to the shaft 6, but are spaced radially therefrom. As shown in Fig. 2, the coil structure 12 includes winding terminals 22 and 24 which extend from the end portion 18 of the coil structure to engage respectively lugs 26 and 28 carried by terminal plates 29a and 29 respectively. The plates 29 and 29a may be supported in any suitable manner and insulated from each other by means of a supporting plate 30 preferably constructed of insulating material and secured to the shaft 6.

In order to permit extension of the winding terminals 22 and 24 to the plates 29 and 2% the supporting plate 30 may be provided with suitable openings 31 and 32 proportioned to receive the terminals 22 and 24 respectively. Additional lug members 33 and 34 may be provided on the plates 29a and 29 respectively with each of the lugs .33 and 34 being bent up from the associated plate adjacent the lugs 26 and 28 respectively. in order to electrically connect the lugs 26 and 33 and the lugs 28 and 34 the plates 29 and 2911 are preferably constructed of suitable electroconductive material.

To facilitate the connection of the coil assembly for energization from an external circuit (not shown) a terminal assembly 35 is provided. The assembly 33 preferably includes a pair of spiral springs 36 and 37 constructed of electroconductive material and wound about the shaft 6 in opposite directions. Insulation of the springs 36 and 37 may be provided by means'of a plurality of insulating barriers 38, 39, 4t) and 41 having hubs 42, 43, 44 and 45, respectively, proportioned to receive a metallic sleeve member 46. The barriers 38, 39, 4t and 41 are arranged on the sleeve member 46 with the hubs 42 and 43 of the barriers 38 and 39 in engagement and with the hubs 44 and 45 of the barriers 40 and 41 in engagement to provide sufiicient space for positioning of the spiral springs between the barriers as shown in Fig. 2. Mounting of the sleeve member 46 relative to the composite shaft 6 will be described hereinafter.

The spiral springs 36 and 37 may be supported in any desired manner. For example, the inner ends of the springs 36 and 37 may be secured respectively to projections 47 and 48 extending from a pair of electroconductive members 49 and 50. The outer ends of the springs 36 and 37 may be ailixed to the terminals of an external circuit (not shown). The electroconductive members 49 and 50 may be supported by the insulating barriers 38 and 40, respectively, and are preferably provided with lugs 49a and 50a. Suitable leads 23 and 25 are provided for the purpose of offering a path for current between the terminal assembly 35 and the electroconductive plate 29. To this end the terminals of the lead 23 are connected to the lugs 33 and 49a whereas the terminals of lead 25 are secured to lugs 34 and 50a.

An indicating pointer 51 may be secured to the composite shaft 6 in any desired manner for cooperating with a suitable scale (not shown).

The stator assembly 2 includes a magnetic structure 52 which establishes magnetic paths for magnetic fluxes produced by currents fiowing in the coil structure 12 and in fixed windings 53 and 54- associated with the magnetic structure 52. As illustrated in Fig. l, the mag netic structure 52 includes a magnetic section 55 having a continuous peripheral portion or rim 56 which surrounds the composite shaft 6 and the coil structure 12. Suitable pole-pieces 58 and 60 project from the rim 56 to provide arcuate pole faces adjacent surfaces of the coil sides 14 and 16. In addition, cantilever arms or cores 62 and 64 project from the rim 56 and pass through the coil structure 12 on opposite sides of the shaft 6. By inspection of Fig. 1, it will be observed that the cores 62 and 64 are spaced in the direction transverse to the shaft 6 by a distance sufficient to permit rotation of the composite shaft 6 therebetween. The cores 62 and 6d are provided with arcuate surfaces spaced from the pole pieces 53 and 60 to provide arcuate air gaps 66 and 63 within which the coil sides 14 and T6 are disposed for movement. In effect, the cores 62 and 64 provde a substantially cylindrical magnetic core which is attached on opposite sides to the rim $6 of the magnetic section and which has a passage 7h extending therethrough of substantially circular cross-section proportioned to accommodate the composite shaft 6.

The magnetic section 55 may be formed of any suitable soft magnetic material, such as silicon iron, having a high magnetic permeability and low hysteresis loss. The magnetic section 55 may be a solid piece. However, it is preferable to form the section 55 of a plurality of magnetic laminations 72, especially if the instrument is employed to measure alternating-current quantities. By inspection of Fig. 1, it is seen that separate magnetic paths are provided for each of the coil sides 14 and 16. For example, the magnetic path of the coil side 14 includes the pole-piece 58 and the core 62 together with the air gap 66. Consequently, when the fixed winding 53 is energized, magnetic flux is directed through the magnetic path to establish a magnetic field for the coil side 14. In a similar manner, the magnetic path of the coil side 16 includes the pole-piece 60 and the core 64 together with the air gap 68. Consequently, when the fixed winding 54 is energized, magnetic flux is directed through this magnetic path to establish a magnetic field for the coil side 16. The fixed windings 53 and 54 may be connected in series circuit relation to be connected for energization either by direct-current quantities or alternating-current quantities. For example, the windings 53 and 54 may be connected for energization in accordance with an alternating voltage of an alternating-current circuit and the coil structure 12 may be connected for energizatiou in accordance with an alternating-current of an alternating current circuit to produce a response representative of power of an alternating-current circuit.

In order to improve the performance of the instrument, an adidtional magnetic section '74 may be added to the magnetic section 55' as described in the aforesaid Lunas patent. The magnetic section 74 is similar in construction to the magnetic section 55, except that the section '74 is reversed relative to the section 55 about axis transverse to the composite shaft 6. The section '74 includes a pair of cores 76 and 78 which extend through the coil structure 12 on opposite sides of the shaft 6. In addition, the section 74 has a pair of pole-pieces it and $2 which are positioned respectively in the wind ings 53 and d4. It will be observed that the cores '76 and 7d are spaced to provide a passage 34 therebetween which corresponds to thepassage 7d of the section By inspection of Fig. 1, it will be observed that the passages 7a and 84 are disposed angularly about the shaft 6 with respect to each other. Consequently, the coil structure 12 cannot be-removed fromthe magnetic structure 52 by a simple movement thereof in the direction of the shaft 6. To permit removal of the coil structure 12 from the magnetic structure 52, the sections and 74 are preferably spaced from each other in the direction of the shaft 6 by a distance sufficient to permit movement of the end portion 18 of the coil structure 12 therebetween when the coil structure has been rotated through an angle of approximately 90 in the counterclockwise direction as viewed in Fig. l, and dropped through the passage 70. The desired spacing may be provided by any suitable spacer constructed of either a magnetic or non-magnetic material. The spacer is preferably divided into two parts 86 and 8% which are spaced to provide an opening M in the magnetic structure. Each of the parts is preferably in the form a plurality of magnetic laminations which are similar in construction to the adjacent parts of the laminations of the magnetic sections 55 and 74. Operations required to assemble and disassemble the instrument are described in detail in. the aforesaid Lunas patent.

In the past, it has been the practice to construct a moving-coil assembly by mounting the coil structure on the coil-supporting shaft with portions of the windings of each end portion of the coil spaced by an amount sufficient to acccmmodate portions of the shaft so that the coil could be mounted concentrically of the associated shaft. The provision of spaces between port ons of the windings has necessitated difiicult winding operations. According to the invention the above difficulties may be overcome by providing a coil-supporting shaft constructed of a plurality of parts and adapted to concentrically support a coil without having portions of the shaft projecting through the ends of the coil. Consequently, the coil may be provided with compact and continuous windings formed by a simple winding operation.

The moving-coil assembly may now be described in detail. Referring to Figs. 2 through 6, the composite shaft 6 is illustrated as comprising a pair of stub shafts 6a and secured to opposing terminals of a central supporting member 6b and disposed along a common axis. The supporting member 6b is illustrated in Figs. 4, 5 and 6. As there shown, the member 6b comprises an elongated block preferably formed of relatively lightweight, non-magnetic material such as aluminum, although any other suitable material may be employed. Dimensions of the member 611 are selected to permit proper positioning thereof within the passages 7d and 84 of the magnetic structure 52.

In order to facilitate the mounting of the coil structure 12 on the member 61) concentrically thereof, an opening or slot 87 is provided in the member 6b to define a loop having side portions 89 and 91 and terminal portions 92 and 94. As clearly shown in Figs. 2 and 3, the opening 87 has an overall length dimension which is slightly greater than the length dimensions of the side portions 14 and 16 of the coil structure 12 in order to permit passage of either of the sides 14 and 16 of the coil structure 12 through the opening $7. As shown in Fig. 4, the opening 87 may be configured to provide a pair of enlarged openings 96 and 98 communicating through a central connecting passage or opening run. The openings 96 and W5 are disposed to receive respectively the end portions 18 and 29 of the coil structure 12. The sides 89 and 911 of the member 6b are recessed to provide two pairs of channels 102 and 10 5- having respectively channel sides 106 and 168. The channel sides 106 are disposed in a common plane while the channel sides This? are disposed in another common plane. It will be observed that the length dimensions of the openings 96 and d8 are slightly greater than the thickness of the end portions 18 and 2d of the coil In addition, the width dimensions of the openings 96 and 98 are larger than the width dimension of the coil 12. The purpose of the chan nels Th2 and 1% will be explained hereinafter.

In order to mount the stub shafts 6a and do on the central support member 6b, the terminal portions 9.2 and 94 of 'the' member 6b are provided respectively with hub portions 110 and 112 having central bores 114 and 116 proportioned to receive the stub shafts 6a and 60 as by a press fit. In addition, the terminal portions 92 and 94 of the member 6b are provided with bores 118 and 120 extending transversely of the central bores 114 and 116 to accommodate wedges which assist in securing the shafts 6a and 60 to the hubs 110 and 112 respectively.

In order to accommodate the supporting plate 30, a face of the terminal portion 92 of the member 6b is provided with a raised portion 122 which supports the plate 30. The plate 30 may be provided with openings proportioned to receive screws or other securing means which extend through openings 124 of the terminal portion 92 to secure the plate 30 to the portion 122 of the terminal portion 92. The terminal assembly 35 may be secured to the stub shaft 6a in any desired manner. For example, the insulating barriers 38, 39, 40 and 41 together with the electroconductive members 49 and 50 and spiral springs 36 and 37 may be mounted on the metallic sleeve 46 as described hereinbefore. The sleeve 46 is provided with a collar 127 and may be detachably secured to the shaft 6a by a removable pin 129 which passes through the shaft and collar. To mount the moving-coil assembly for rotation the shafts 6a and 60 may be provided with apertures 128 and 130 proportioned to receive pivots 128A and 130A which engage the bearing screws 8 and 10.

As shown in Fig. 3, the coil structure 12 includes a plurality of windings 132 which are preferably wound on a coil form 134 disposed in a loop of substantially rectangular configuration to provide the coil sides 14 and 16 and connecting end portions 18 and 20. If desired, the windings 132 may be removed from the coil form 134 upon completion of the winding operation and embedded within a plastic mass to provide a complete coil structure. However, it is desirable to retain the coil form 134 to provide a rigid assembly and to provide means for damping movement of the coil assembly. As best shown in Fig. 3, the coil form 134 is provided with a channelled peripheral portion in order to facilitate the winding operation and to retain the windings in position. For the purpose of damping the moving-coil assembly, the coil form 134 is preferably constructed of a suitable electroconductive material such as aluminum which is effective to produce a damping torque upon rotation of the coil structure 12 relative to the magnetic structure 52.

In order to assemble the moving-coil assembly, the coil structure 12 is inserted in the opening 87 of the support member 6b to have portions of the end portions 18 and 20 thereof positioned within the enlarged openings 96 and 98 as shown in Fig. 2. Suitable plates 136 and 138 may then be positioned within the openings 96 and 98 to be supported by the channel sides 106 and 108, respectively, of the channels 102 and 104. The plates 136 and 138 may be constructed of any suitable material such as a phenolic resin and are preferably formed to have length dimensions substantially equivalent to the thickness of the support member 6b. With the plates 136 and 138 positioned as described, the openings 96 and 98 are effectively isolated from the connecting passage 100 whereby securing means 140, preferably of insulating material, may be introduced into the openings 96 and 98 to secure the coil structure 12 to the supporting member 6b. The securing means may comprise a suitable hardenable fluid material such as a cement or adhesive capable of holding the coil structure firmly on the support memher after it hardens. Conveniently, the coil structure 12 may be held manually or by means of a suitable fixture with the sides 14 and 16 of the coil structure spaced equal distances from the common axis defined by the stub shafts 6a and 60 while the material 140 hardens to provide a symmetrical coil assembly.

The moving-coil assembly herein described is desirable for an electrodynamometer instrument as herein described, but it is particularly desirable for an instrument requiring a low-loss coil, such as a permanent-magnet moving-coil instrument. If the instrument of Fig. l is to be a permanent-magnet, moving-coil instrument, at least portions of the magnetic structure would be constructed of permanent-magnet material polarized to produce magnetic fields in the air gaps. A suitable magnetic structure of this type is shown in Patent 2,508,439 which issued May 23, 1950.

Although the invention has been described with reference to certain specific embodiments thereof, numerous modifications are possible and it is desired to cover all modifications falling within the spirit and scope of the invention.

I claim as my invention:

1. The method of assembling an instrument movingcoil assembly comprising the steps of forming a pair of openings and a passage connecting said openings in a coilsupporting member, winding a coil with side portions and end portions connecting the side portions, passing a side portion of the coil through the openings and connecting passage to position a portion of each end portion of the coil within a separate one of said openings, isolating each opening from the connecting passage, and introducing a hardenable fluid into each of said isolated openings.

2. An instrument moving coil assembly comprising a coil supporting member having a pair of spaced enlarged openings communicating through a restricted connecting passage defining a pair of spaced wall portions of each opening, each pair of wall portions being included in a common plane substantially transverse to the direction of extension of the connecting passage, a coil having side portions and end portions connecting the side portions, said coil being positioned relative to the supporting member with a portion only of each end portion within a separate one of the openings to have the side portions spaced from the connecting passage, a separate plate member bridging each pair of wall portions to isolate each opening from the connecting passage, and a hardenable fluid material substantially filling each opening to connect the end portions and the supporting member.

3. An instrument moving-coil assembly comprising a coil disposed in a first loop defining a first plane, a coilsupporting member disposed in a second loop defining a. second plane substantially perpendicular to the first plane, said first loop being positioned within the opening defined by the second loop, bearing means secured to the second loop externally of said opening for mounting the coil for rotation about an axis substantially coinciding with the intersection of said planes, said coil being of selfsupporting hollow rectangular configuration including a pair of parallel side portions on opposite sides of said axis when the coil is in operative position within said opening, and a pair of end portions connecting the side portions, said opening being of sufiicient size to permit movement of the end portions of said coil thereinto for assembling said coil into the coil supporting member in operative position, each of said parallel side portions being spaced from the coil-supporting member in a direction radially of said axis by a substantial space when the coil is in its operative position, and separate means engaging each of the end portions and the supporting member at opposite ends of the opening for securing each of the end portions to the coil-supporting member.

References Cited in the file of this patent UNITED STATES PATENTS 1,503,255 Stoekle July 29, 1924 1,927,346 Lawrence Sept. 19, 1933 2,457,685 Kleep Dec. 28, 1948 2,508,379 Freedman May 23, 1950 2,508,439 Young May 23, 1950 FOREIGN PATENTS 599,247 Great Britain Mar. 9, 1948 

